The present invention relates to a fuel management computer for an aircraft and more particularly to a preprogrammed timing mechanism for notifying a pilot when to adjust the fuel selector valve to begin using a different fuel tank.
Recent studies of aircraft accidents indicate that fuel starvation was a cause or related factor in a substantial number of cases. The most frequently cited causes of fuel starvation include exhaustion of fuel from the tank in use while ample fuel for continued operation remained in other tanks on the aircraft and incorrect positioning of the fuel selector valve.
Often, if a pilot forgets to switch fuel tanks before the tanks are exhausted, the engine may not be restarted in sufficient time to prevent an accident. Aircraft manufacturers have become greatly concerned about the apparent lack of attention to fuel supply which is apparent from the number of accidents resulting from the exhaustion of one tank of fuel while ample fuel remained in another tank on the aircraft. One solution to the problem is better education of pilots about fuel management. Various manufacturers, however, have indicated a substantial need for a low-fuel warning device which could be used to alert a pilot of impending fuel starvation.
The problem of fuel starvation is particularly acute in single engine and twin engine airplanes. Generally speaking, single engine planes have two fuel tanks and twin engine planes have four fuel tanks. The fuel tanks are located on the left and right wings of the plane. The pilot may operate a fuel selector valve to select which of the tanks is to be used for supplying fuel to the engine at any given point of time during the flight.
In the case of a single engine aircraft having two fuel tanks, in order to maintain proper balance of the aircraft in flight, it is necessary to draw fuel from one tank and, after a predetermined period of flying time, switch the fuel selector valve to draw fuel from the second tank. After a third predetermined period of flying time, the pilot must turn the fuel selector valve back to the first tank and leave it there for the remainder of the flight. The Federal Aviation Agency requires that an airplane must land with a 45 minute reserve of fuel when flying IFR (instrument flight rules) and a 30 minute reserve of fuel when flying VFR (visual flight rules). In order for a pilot to properly manage the fuel of a single engine aircraft to maintain proper balance of the aircraft in flight, as well as comply with the FAA regulations, it has been found desirable to draw fuel from a single engine - two- tank airplane having a total flying time of 4 1/2 hours in three modes.
The first mode for a two-tank system provides for the withdrawal of fuel from the first tank for 0.75 hours to allow a reserve of fuel in the tank for flying 3.75 hours. In the second mode, the fuel selector valve may be switched to draw fuel from the second tank for 2 hours. In the third and last mode, the fuel selector valve may be switched back to the first tank to draw fuel from it for the remaining 1 hour of the flight. The management of the fuel in these three modes allows the pilot to land with an amount of fuel provided for by the FAA regulations. The tabulations of the three modes in this example is as follows: